All those who are interested in Astronomy know about the importance of the Hubble Space Telescope (HST).This telescope started a new Era in the world of Astronomy and Astrophysics. By staying far above the Earth's atmosphere it captured thousands of spectacular images of planets, stars, galaxies and cluster of galaxies, improving our understanding about the evolution of the Solar System, Galaxies and the Universe.
Lagrangian PointsWhy such a far positioning is required? Well, for this let us understand what a Lagrangian Point is. In space Gravity rules. The Moon revolves about the Earth because of the gravitational pull of the Earth. The Earth is bound by the gravitational pull of the Sun. In the cited example the Moon is under the control of the Earth and the Earth is in control of the Sun. The Sun is not directly controlling the Moon, but just the Earth because the Moon is nearer to the Earth than the Sun. In other words, the gravitational field of any mass is stronger in its surrounding.
Actually, the amount of gravitational bonding between two bodies is determined by the masses of both the bodies and the distance between them. But, if the mass of one of the two bodies is negligible, it is assumed that massive body will rule over the second one.
Let us understand this with an analogy of Magnets. Suppose, two huge magnets with equal power are suspended with the help of strings what will you see? Both the magnets will be seen to be attracting each other if the facing poles are opposite. But, if one of the magnets is very small then only the smaller magnet will go near the larger one which will not even move.
Instead of the Moon if we consider a small mass object like rocket, it will remain in the control of the Earth if it is near to it, but if the rocket is very far from the Earth, the chances are that the Sun takes over the control of the rocket. We know what happens when the rocket is near to the Earth and also when it is very far. This indicates that there should be a region between two gravitating bodies where the net gravitational force of the bodies cancels each other. This region is known as Lagrangian Point. The term Lagrangian is used to honour Joseph-Louis Lagrange, the founder of this principle.
In the year 1772, the Italian-French mathematician Joseph-Louis Lagrange was working on the famous three-body problem when he discovered this through the results. The scope of this article is not enough to explain the concept of the three-body problem. Lagrange found five specific fixed points around two bodies where the third body experiences zero net force. These points are knows as L1, L2, L3, L4 and L5. The accompanying figure shows the location of these points.It is now clear that the Sun-Earth system has 5 Lagrangian points and JWST shall be placed at L2. Anything placed at these points can principally stay there until the Sun and the Earth remains. But, the stability of all the five regions is not same. The point L3 of Sun-Earth system is considered to be the weakest one because the planet Venus after every 20 months comes very near to L3 disturbing the stability of the region.
At the point L2 there is one more benefit. This region always remains in the shade of the Earth giving a natural shield from the intense radiation and other harmful effects of the Sun. Being this far also keeps the JWST away from the Earth's atmosphere and its own radiation in optical as well as infra-red wavelength. The point L2 is shown in Fig. 2.
At present Wilkinson Microwave Anisotropy Probe of NASA is already at the Sun-Earth L2 point. Like JWST two other probes are planned to be placed at L2. The names of these two probes are Herschel Space Observatory and the Gaia Probe. The Earth-Moon L2 is a good location for a communication satellite covering the Moon's far side.
MirrorAs stated earlier, JWST will have a mirror that shall detect infrared radiation unlike HST which captures the light in optical wavelength. The JWST mirror is a beryllium reflector with a diameter of 6.5 meters (650 inches). This makes JWST's light collecting area 6 times larger than HST. As this diameter is much larger than any current launch vehicle, the mirror is composed of 18 hexagonal segments, which will unfold once the telescope is placed properly at its determined location.
The engineers at NASA and other space agencies have made several inventions to be incorporated in to JWST. Thousands of Microshutters will be incorporated into the optics of the primary mirror. Each microshutter will be 100 to 200 nanometers. An array of 62,000 shutters will sit in the front of the infrared detector. These microshutters will allow the telescope to focus on the faint light of stars and galaxies even if they are adjacent to bright objects.
MissionThe JWST's primary scientific mission has four main components: to search for light from the first stars and galaxies which formed in the Universe after the Big Bang; to study the formation and evolution of galaxies; to understand the formation of stars and planetary systems; and to study planetary systems and the origins of life.After a commissioning period of approximately 6 months, the observatory will begin the science mission, which will be required to last a minimum of 5 years. The potential for extension of the science mission beyond this period exists, and the observatory is being designed accordingly.
Statistics at a GlanceJWST will be placed 15 lakh kilometers away from the Earth in L2 of Sun-Earth. The approximate launch date if June 2013. The mission is of 5 years but the goal is of 10 years. The total mass of JWST is 6,200 kilograms. The primary mirror is 6.5 meters in diameter with a total light collecting area of 25 m^2. The focal length of the mirror is 431.1 feet. For more information about JWST visit the NASA's website http://www.jwst.nasa.gov/.
Refer to the article on Hubble Space Telescope in the same magazine's issue 4 Volume 2 for details regarding its history and working.
But let us have a glimpse here of HST for a quick refresh. HST was launched in the year 1990 and since than it has required a few repair-missions. Obviously, any machine would require some kind of repairing if it is working for almost 17 years, that too, without direct human intervention. Even today HST is working fine and shall work for coming 2 to 5 years as estimated by the scientists and engineers operating it. What shall happen when HST stops functioning or due to its bad condition it is brought down?
Keeping that in mind scientists have started working on a new space telescope known as James Webb Space Telescope (JWST). The three biggest space agencies are building JWST. These agencies are NASA, ESA and CSA. JWST is scheduled to be launched no earlier than June 2013 on Ariane 5 rocket.
Formerly, JWST was called Next Generation Space Telescope (NGST): later it was renamed to James Webb Space Telescope (JWST) honouring NASA's second administrator, James E. Webb, in 2002.
MirrorJWST is an infrared observatory unlike HST which is an optical one. It means that while HST can capture those images which our eye can perceive, JWST is designed to capture light that the human eye cannot perceive. In other words, JWST will look at such a segment of the spectrum which HST cannot detect, this segment is known as Infrared. It is basically less energetic than the optical wavelength requiring more sophisticated and technologically advance systems to detect. Due to this even the objects that are far or dwarf stars or exoplanets planets which go about dead stars come in the range of JWST. Principally, every object generates infrared radiation. But for an object to radiate in optical wavelength, it requires special conditions like either reflecting of light (planets) or generating light of its own by the means of Nuclear Fusion (stars). This makes JWST more penetrating!
PlacementAnother difference between HST and JWST is in their distance from the planet Earth. JWST shall be placed at a distance of about 15 lakh kilometers. This is beyond the Moon's orbit. Moon is at an average distance of 3.84 lakh kilometers.
Lagrangian PointsWhy such a far positioning is required? Well, for this let us understand what a Lagrangian Point is. In space Gravity rules. The Moon revolves about the Earth because of the gravitational pull of the Earth. The Earth is bound by the gravitational pull of the Sun. In the cited example the Moon is under the control of the Earth and the Earth is in control of the Sun. The Sun is not directly controlling the Moon, but just the Earth because the Moon is nearer to the Earth than the Sun. In other words, the gravitational field of any mass is stronger in its surrounding.Actually, the amount of gravitational bonding between two bodies is determined by the masses of both the bodies and the distance between them. But, if the mass of one of the two bodies is negligible, it is assumed that massive body will rule over the second one.
Let us understand this with an analogy of Magnets. Suppose, two huge magnets with equal power are suspended with the help of strings what will you see? Both the magnets will be seen to be attracting each other if the facing poles are opposite. But, if one of the magnets is very small then only the smaller magnet will go near the larger one which will not even move.
Instead of the Moon if we consider a small mass object like rocket, it will remain in the control of the Earth if it is near to it, but if the rocket is very far from the Earth, the chances are that the Sun takes over the control of the rocket. We know what happens when the rocket is near to the Earth and also when it is very far. This indicates that there should be a region between two gravitating bodies where the net gravitational force of the bodies cancels each other. This region is known as Lagrangian Point. The term Lagrangian is used to honour Joseph-Louis Lagrange, the founder of this principle.
In the year 1772, the Italian-French mathematician Joseph-Louis Lagrange was working on the famous three-body problem when he discovered this through the results. The scope of this article is not enough to explain the concept of the three-body problem. Lagrange found five specific fixed points around two bodies where the third body experiences zero net force. These points are knows as L1, L2, L3, L4 and L5. The accompanying figure shows the location of these points.It is now clear that the Sun-Earth system has 5 Lagrangian points and JWST shall be placed at L2. Anything placed at these points can principally stay there until the Sun and the Earth remains. But, the stability of all the five regions is not same. The point L3 of Sun-Earth system is considered to be the weakest one because the planet Venus after every 20 months comes very near to L3 disturbing the stability of the region.
At the point L2 there is one more benefit. This region always remains in the shade of the Earth giving a natural shield from the intense radiation and other harmful effects of the Sun. Being this far also keeps the JWST away from the Earth's atmosphere and its own radiation in optical as well as infra-red wavelength. The point L2 is shown in Fig. 2.
At present Wilkinson Microwave Anisotropy Probe of NASA is already at the Sun-Earth L2 point. Like JWST two other probes are planned to be placed at L2. The names of these two probes are Herschel Space Observatory and the Gaia Probe. The Earth-Moon L2 is a good location for a communication satellite covering the Moon's far side.
MirrorAs stated earlier, JWST will have a mirror that shall detect infrared radiation unlike HST which captures the light in optical wavelength. The JWST mirror is a beryllium reflector with a diameter of 6.5 meters (650 inches). This makes JWST's light collecting area 6 times larger than HST. As this diameter is much larger than any current launch vehicle, the mirror is composed of 18 hexagonal segments, which will unfold once the telescope is placed properly at its determined location.
The engineers at NASA and other space agencies have made several inventions to be incorporated in to JWST. Thousands of Microshutters will be incorporated into the optics of the primary mirror. Each microshutter will be 100 to 200 nanometers. An array of 62,000 shutters will sit in the front of the infrared detector. These microshutters will allow the telescope to focus on the faint light of stars and galaxies even if they are adjacent to bright objects.
MissionThe JWST's primary scientific mission has four main components: to search for light from the first stars and galaxies which formed in the Universe after the Big Bang; to study the formation and evolution of galaxies; to understand the formation of stars and planetary systems; and to study planetary systems and the origins of life.After a commissioning period of approximately 6 months, the observatory will begin the science mission, which will be required to last a minimum of 5 years. The potential for extension of the science mission beyond this period exists, and the observatory is being designed accordingly.
Statistics at a GlanceJWST will be placed 15 lakh kilometers away from the Earth in L2 of Sun-Earth. The approximate launch date if June 2013. The mission is of 5 years but the goal is of 10 years. The total mass of JWST is 6,200 kilograms. The primary mirror is 6.5 meters in diameter with a total light collecting area of 25 m^2. The focal length of the mirror is 431.1 feet. For more information about JWST visit the NASA's website http://www.jwst.nasa.gov/.
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